The present invention relates to winch control valves and more particularly relates to control valves for winch transmissions having a normally disengaged, pressure-engageable clutch and a normally spring-engaged, pressure-releasable brake.
The hydraulic control systems for these transmissions are often of a basic type including a directional control valve comprising a valve spool movable to a hold position wherein the brake is engaged and the clutch is disengaged, a wind-in position wherein the brake is disengaged and the clutch is engaged, and a free spool position wherein both the brake and clutch are disengaged. In some prior art for winch transmissions of this basic type of design, the control valve for the winch operates so as to vary the hydraulic fluid pressure routed to the hydraulic brake to thereby establish a controlled release condition in the winch drum so that loads on the winch cable could be lowered at a controlled rate. Such a control valve is disclosed in U.S. Pat. No. 3,529,702, issued to Eckstein, Jr. on Sept. 22, 1970.
A desirable feature which is incorporated in some more complex winch transmissions and controls therefor is that of providing for a controlled wind-in of the cable which permits the winch drive to slip when a predetermined load exists on the cable to thereby eliminate cable breakage and other damage when a load being winched in becomes caught by an immovable object or engages the rear of the vehicle. This mode of operation is sometimes called an inching mode.